Oral administration of a drug provides a plasma level time profile of a drug or its active or inactive metabolite, which can be modulated by the design of the drug delivery system or dosage form.
Drug delivery system or dosage forms have been designed in various ways, depending on the requirements of the therapy or the needs of the patient. For example, the formulations may be designed to include a coating for the purpose of protecting the drug from the environment or prevent the release in the oral cavity and interaction of the drug with taste buds and yet release the drug instantly and rapidly in the stomach by dissolution of the coating in the gastric fluid. Instant and rapid release of the drug enables quick onset of action. These systems depend on pH-dependent coatings, which will not dissolve in the salivary fluids but dissolve readily in the gastric fluids. However, systems that depend on pH-independent coatings but can perform the same function are not available.
Drug delivery systems releasing the drug slowly over longer duration have been traditionally used to improve therapy by                improving patient compliance to dosage regimens through the decrease in the number of doses the patient has to take in a day, by providing desired effective plasma levels for therapeutic efficacy over the duration of therapy for example throughout the day including at night when the patient is asleep;        decreasing peak plasma levels when they are associated with side effects;        reducing side effects in chronic therapy by reducing the fluctuation in plasma levels seen after multiple dosing of conventional rapid release systems;        when the drug has local action on the gastrointestinal mucosa, to spread the release spatially over the whole of the gastrointestinal mucosa as the drug delivery system is transported in the mucosa by the motility of the gastrointestinal tract.        
Drug delivery systems are also designed to release the drug at specific site in the gastrointestinal tract by use of pH-dependent coatings that dissolve in the pH environment at the specific gastrointestinal site. There is a need for designing cores for such coated systems wherein the cores provide rapid release without substantial delay over the specific site or region, for example a release initiated over a period of 1 minute to 30 minutes after encountering the particular site or pH. There is also a need for designing cores for such site-specific coated systems wherein the cores are designed to provide controlled release over the specific region, for example from the colon to the rectum.
We have designed novel core coated oral drug delivery systems that utilize novel technology for reliably removing the coating fully or partially from one or more preselected surfaces of the system upon contact with an aqueous environment. This novel technology can be gainfully employed in any of the above-described drug delivery systems to meet specific objectives of therapy.
U.S. Pat. No. 4,839,177 (the '177 patent) discloses a system for controlled-rate release of active substances consisting of (a) a deposit core of a defined geometric form, comprising a polymeric material having a high degree of swelling and a gellable polymeric material, and (b) a support platform consisting of a polymeric material insoluble in aqueous fluids applied to the deposit core such that it partially coats the deposit core. The trademark, Geomatrix®, refers to this system. The disadvantage of this system is that the rigid support platform can crack or flake before the active substance is completely released. U.S. Pat. No. 5,422,123 is an improvement over the '177 patent in that the support platform consists of polymer substances, which are slowly soluble and/or gellable in aqueous fluids, and plasticisers, such that the support platform does not crack or flake before the drug is completely released from the deposit core. Although the patents disclose systems wherein surface area of release is reduced by covering two or more surfaces of the deposit core, in practice such systems are difficult to manufacture at an industrial scale—especially systems wherein two lateral surfaces and one planar surface are coated by the support platform. For example, in example 2 of the '177 patent, the barrier layers were applied by immersing the core in a polymeric solution as far as the edge of its upper base, such that two lateral sides and one planar surface of the core are coated. In example 3 of the '177 patent, the barrier layers were coated on the lateral sides of the core by spraying or brushing the polymeric solution onto the sides. These methods, although possible on small experimental scale, are not feasible and reproducible on an industrial scale.
U.S. Pat. No. 5,650,169 provides a pharmaceutical tablet capable of releasing the active ingredients contained therein at subsequent times, the tablet being prepared by a process wherein a three-layered tablet core comprising a first drug-containing layer, an intermediate barrier layer and a third drug-containing layer are covered with an impermeable polymeric film. The first layer presents a raised top, which is removed by abrasion so as to allow contact of the abraded first layer surface with the environment. The composition of the barrier layer is designed to modulate release from the third layer of the tablet. A major disadvantage of this system is that it requires removal of the raised top layer by abrasion to provide a means for release of the components of the system. This may not be feasible at an industrial scale. Further, if the abrasion is not uniform, the release of the active ingredients will be affected.
U.S. Pat. Nos. 6,720,005 and 6,733,784 relate to coated, platform-generating tablets. The tablet hydrates and expands upon swallowing such that the membrane covering the coating ruptures mostly around the belly-band surface of the tablet due to swelling of the core, thereby exposing the belly surface of the core tablet to hydrating and eroding liquids. A disadvantage of the system is that the coating is not reliably removed from the belly-band surface always but may rupture at a different weak point. Thus, the surface area of exposure may vary. Also, the systems show a lag time of release of half an hour or more. Many shapes of the core have been suggested in the invention but some of these may accentuate the problems encountered during tablet manufacture. Also, the belly-band surface, which is exposed after the coating ruptures, has the least surface area and other more preferred surfaces are not exposed.